1. Technical Field
The present disclosure relates to a light emitting device, and more particularly, relates to a light emitting device used as a vehicle lamp.
2. Background
Conventionally, vehicle lamps using a semiconductor light emitting element such as Light Emitting Diodes (LEDs) as a light source have been known. When LEDs are used as a light source for vehicle lamps, a lamp constitutes the eye of a vehicle, and the aspect of the design is regarded as important Thus, the specifications thereof can be classified into a wide variety of types. For example, different vehicles (e.g., car models) have different numbers of LEDs to be used, different shapes and sizes of the lamp itself or different configurations of the lighting control circuit of the vehicle lamp for turning the light on/off, and for controlling the brightness of each LED. Thus, there may be many variations thereof.
In cases where one-to-one circuit development is carried out for the different configurations, huge development costs inevitably are required. For example, to configure a system where one circuit is adapted to multiple LEDs, the driving circuit must be configured according to the type of the LEDs or according to the car model. Thus, an increase in cost of the product is incurred with an increase in circuit development cost.
Under such circumstances, there has been proposed a system adopting the following configuration so as to attain standardization, reduction of development cost, and cost reduction. Multiple light units each including a LED, a switching regulator and a control circuit are provided. In addition, a control unit includes an input circuit for supplying a DC power source from a battery to each light unit, a microcomputer for controlling each light unit, and a peripheral circuit. Thus, the control unit and each of the light units are connected through a feed line and a communication line (see e.g., Japanese Unexamined Patent Publication: JP-A-2006-73400).
According to JP-A-2006-73400, the control unit and each of the light units are connected to each other through a communication line as well as a feed line. Therefore, the operation for wiring the feed line and the communication line becomes more complicated with an increase in the number of light units, resulting in an increase in cost and an increase in the number of mounting steps. In this case, to simplify the wiring of the communication line, a serial communication system such as a Local Interconnect Network (LIN) is employed. However, when this kind of serial communication system is employed, it is necessary to assign an address to each light unit, which makes standardization more difficult.